Cells efflux cholestrol and phospholids to apolipoproteins such as apoA-l as part of a process that maintains whole body lipid homeostatsis. The physiologic importance of lipid efflux is demonstrated by patients suffering from Tangier disease, a rare genetic condition characterized by peripheral neuropathy, premature cardiovascular disease and an absence of circulating HDL. Genetic mapping studies have associated the Tangier phenotype with mutations in the ATP binding cassette transporter ABCA1 and subsequent studies have shown that ABCA1 plays a rate limiting role in the formation of HDL. In the general population elevated HDL levels are inversely correlated with the incidence of cardiovascular disease, thus therapies that increase ABCA1 activity may help prevent disease progression. The objective of this proposal is to describe key structure-function relations that define the ABCA1 efflux mechanism and what role protein-protein interactions play in determining the activity of ABCA1. This broad aim is focused by the analysis of a naturally occurring Tangier mutation that deletes the last 46 amino acids of the transporter. The deleted amino acids are part of a highly conserved domain, and as shown in this proposal, are essential for ABCA1 efflux activity. Analysis of additional synthetic mutants within the deleted region has defined a novel VFVNFA motif that uniquely identifies a subclass of ABCA transporters. This motif is essential for ABCA1 activity and can act in trans to inhibit efflux activity. A proteomic approach has been developed in which ABCA1 and interesting mutant transporters are affinity purified and the co-purify proteins are analyzed by mass spectrometry. The proteins which interact with the VFVNFA motif are described and their functional relevance to the efflux mechanism investigated will be investigated. Since a set of the interactions appear to down-regulate efflux activity disruption of such interactions may offer therapeutic targets by which ABCA1 efflux can be increased. [unreadable] [unreadable]